1. Field of Invention
The present invention relates to processing tank bottom wastes, pit wastes, and other petroleum-based sludges to produce products that meet refinery standards and improve environmental attributes.
2. Background
In recent times tank bottom wastes, sometimes referred to as sludge and often shortened to just tank bottoms, have become an increasing problem since their regulation has often classified them as environmentally hazardous wastes with the corresponding difficult and expensive handling problems. However by appropriate processing this designation can disappear and the resulting constituents become potential product material or can be disposed of in an ordinary manner. Additionally their composition, being a mixture of crude oil, solids, and water, is unacceptable for refineries which would require the removal of significant portions of solids and water.
The amount of this potential tank bottom waste builds to large quantities not only because of the large oil field, pipe line, and refinery capacities in this country, but also because of the storage of these tank bottoms until some disposal method can be employed. Particularly in remote oil fields far from refineries, storage has continued for many years.
Earlier attempts at processing such tank bottoms often employed several common approaches. Filtration using standard commercial filter presses has been accomplished for some tank bottoms that were easily pumpable and oil recovery was significant as well as producing a solid, easily disposable residual. For further enhanced recovery of useful products, solvent extraction was employed particularly if the unit is operated in conjunction with a refinery where such a solvent stream, such as propane, is readily available. The resultant extracted stream then was returned to the refinery for further processing of the extracted oil. The solvent extraction was utilized on the filter cake from premechanical treatment or employed directly into the tank before pumping. Additionally sometimes bioremediation is utilized to treat such tank bottoms both directly and indirectly.
Prior art United States patents covering the above mentioned tank bottoms processing include:
______________________________________ U.S. Pat. No. Inventor Year ______________________________________ 5,022,992 Looker 1991 4,927,530 Ueda 1990 4,897,205 Landry 1990 ______________________________________
Referring to the above list, Looker discloses a sludge removal apparatus with sloping tank sides and recirculation with an appropriate skimmer designed to remove floating sludge paint particles from water. Ueda discloses a processing unit employing anaerobic bacteria to treat excess sludge from sewage water treatment or other sludge-type material that is acted upon by such bacteria. Landry discloses a process for treating waste material employing steam and recirculated liquid to lower the viscosity of the waste material, such as liquid hydrocarbon and solids, in order to allow removal and subsequent separation by settling; this is particularly used for cleaning tanks.